Enteric Gram-neg (part 1) Flashcards
ENTEROBACTERIACEAE
What is the medical importance of the enteric family?
Indicator of fecal pollution of water
30% of hospital acquired cases (nosocomial infection)
Easily studied genetically
Difficult to treat with antibiotics
Physical characteristics of Enterobacteriaceae
Gram-neg, medium sized rods
Flagella if mobile
Non spore forming anaerobes
What are some non-motile Enterobacteriaceae?
Klebsiella and Shigella genus
Cultural characteristics of Enterobacteriaceae
Ferment glucose
Resistant to acid and bile
What makes Enterobacteriaceae toxic?
Lipid A
Lipid A + O polysaccs=Lipopolysaccharide (endotoxins) –> on their cell wall
Selective media used for Enterobacteriaceae
Unioculated MacConkey
Which Enterobacteriaceae are lactose fermenters?
E. coli, Klebsiella, Enterobacter
with a pink pigmentation
Which Enterobacteriaceae are non-fermeters?
Salmonella, Shigella
with straw colored colonies
What are gram inhibitors?
Dye crystal violet that suppresses unwanted Gram-pos organisms by bile salt or bacteriostatic dye
Triple Sugar Iron (TSI)
Indicator media
Tests organisms for carb fermentation, gas production, hydrogen sulfide production
How do you categorize TSI?
Black= H2S
Cracks= Gas
Red slant= glucose used (no lactose and peptones used)
Yellow= all sugars fermented
How is salmonella and proteus classified by the TSI?
Slant= alkaline (red)
Butt= acid (yellow)
Gas (cracks) and H2S (black) positive
How is Enterobacteriaceae divided?
- Major pathogens
- Opportunistic pathogens
- Organisms of uncertain significance
Major pathogens
Salmonella
E. coli
3 Yersinia species
Opportunistic pathogens
Klebsiella, Enterobacter, Proteus, Edwardsiella, Citrobacter, Morganella, Shigella
There are over ______ genera and over ______ species
40
180
Escherichia coli (E. coli)
Ferments lactose
165 O chains, 50 H (flagella), 90 K (capsules) strains = over 1000 strains
Habitat of E. coli
Large and small intestine of mammals
Excreted in feces and can survive in dust, water and fecal particles for months
E. coli in water= fecal pollution
Adhesions
Fimbira/pili
Mediate adherence to the target cells (glycoprotein) in the GI tract
Capsules
Protects E. coli from complement cascade and inhibits microbe from attaching to phagocytic cells
What enterotoxins does E. coli produce
Heat liable toxin (LT)
Heat stable (STa and b)
Entero-aggregative heat stable (EAST 1)
How do enterotoxins affect cells?
Affect control of cyclic nucleotide activity within the affected cell –> deregulation of water and electrocytes
Predisposing causes of E. coli
Neonates obtaining insufficient Abs from colostrum
Intensive husbandry system
Poor hygiene
Stress factors
Why are neonates susceptible to E. coli?
Normal flora of intestine not fully developed
Naive immune system
Receptor for adhesions of enterotoxigenic present @ 1st weeks of calf life and 6 weeks for piggies
White Scours (Colibacillosis) in young calf
1-5 days: E. coli
5-14 days: Rota- corona virus
10-30 days: Cryptospordium parvum
Any age; Salmonellosis, C. perfringens
Edema disease in young weaning pig
Recent change in feed (lose maternal Abs)
Mild diarrhea noticed few days before
How is E.coli classified?
E. coli causing intestinal disease or extra-intestinal disease
Which E. coli strains cause intestinal disease
Enterotoxigenic E. coli (ETEC) &
Attaching and Effacing E. coli (AEEC)
|
v
Enteropathogenic E. coli (EPEC) &
Vero- Shiga- toxin producing strains (VTEC or STEC)
|
v
Enterohemorrhagic E. coli (EHEC) &
Strains of E. coli causing edema disease
Enterotoxigenic E. Coli (ETEC)
Neonatal calibacillosis in calves, lambs and piglets - first week of life
Host specific
Produces watery diarrhea
Pathogenicity of Enterotoxigenic E. coli
Adhesion followed by production of enterotoxins
Adherence mediated by fimbriae in pigs and calves
Fimbrae receptors for Enterotoxigenic E. coli
F4 (K88), F5(K99), F6(987p), F17, F18, F41
What is significant about Enterotoxigenic E. coli?
No gross or microscopic damage to enterocytes
Toxins within Enterotoxigenic E. coli
LT (heavier)- stimulates cAMP causing secretions of fluids K+, Cl-, enterocytes
ST (smaller)- deregulate cGMP causing fluid and e-accumulation in bowel lumen
Enteropathogenic E. coli (EPEC)
Within attaching and effacing E. coli (AEEC)
Causes muccoid diarrhea in piglets, lambs and pups by erasing normal structure of intestinal vili (no absorption and losing electrolytes and fluid)
What are virulence factors of enteropathogenic E. coli encoded by?
Pathogenic island called enterocyte effacement
Intimin
A key signaling factor of enteropathogenic E. coli that promotes close attachment of E. coli with enterocytes
Shigatoxigenic E. coli (STEC or VTEC)
Edema disease in pigs associated with O139 and O141
Hemolytic and produce shiga toxin
O139 and O141 strains
Present in the large intestine of pigs
Multiply rapidly under conditions of stress (change in diet)
What are the 2 subtypes of the shiga toxin?
STx1 and STx2 (STX2e is associated with the edema disease in pigs)
What does shigtoxigenic E coli target?
Endothelial cells of small arteries of the forehead, eyelids and mesentary
What produces the shigo disease?
Heavy grain diet –> doesn’t produce enough saliva –> makes it easy for the bacteria to invade
Enterohemorragic E. coli (EHEC)
Cause of food poisoning in humans
Associated with cases of hemorrhagic enteritis in calves
What does eneterohemorragic E. Coli do?
Binds and effaces microvilli and produces shiga toxin
Damages adjacent cells and enters circulation
What strains cause extra-intestinal disease?
Septicemic E. coli (SEPEC)
Uropathogenic E. coli (UPEC)
Avian pathogenic E. coli (APEC)
Mammary pathogenic E. coli (MPEC)
Septicaemic E. coli
Frist step: adherence to the intestinal lining
Fimbriae, capsule, aerobactin (iron), endotoxin, colicin V, cytotoxic necrotizing factor, cytolethal factor
How do you diagnose enterotoxins ST and LT?
ELISA
How do you diagnose fimbral antigens?
Latex plate agglutination
Diagnosis of EPEC E. coli
Demonstration of urease production
Ileum shows distortion of microvilli and effacement of mucosal surface
Diagnosis of edema disease
Clinical and post-mortem findings
Isolates are hemolytic
Antimicrobial resistance
Resistance to at least 2 classes of antimicrobial agents is common in vet med
Emergence of fluoroquinolone resistance
How do you determine resistance?
Disc diffusion method or MIC for broth dilutions
The genus enterobacter
Gram-neg bacilli, short and motile
Recovered from bovine mastitis, navel ill/neonatal septicemia, equine uterine infection, canine UTI
Opportunistic pathogens under enterobacter?
Enterobacter aerogenes and E. cloacae
Diagnosis of enterobacter
Recovery of agent from clinical material and ID by biochem tests
What is enterobacter resistant to?
Ampicillin, cephalothin and tetracyline
The genus citrobacter
Widely distributed in the environment (soil, water)
Citrobacter rodentium
Transmissible murine colonic hyperplasia
Where is citrobacter found?
Colon (descending) and cecum –> thickened mucsosa and increasing bowel size
Diagnosis of citrobacter
PCR and culture
